Body Fluids and Homeostasis PDF

Body Fluids and Homeostasis Dr. Menna Elmenyawi  Body Water The Total Body Water (TBW) represents about.60% of the total body weight :TBW is variable infant: 73% male adult: 60% female adult: 40-50% Old age 45% Percentage of the water in the body...

Body Fluids and Homeostasis Dr. Menna Elmenyawi  Body Water The Total Body Water (TBW) represents about.60% of the total body weight :TBW is variable infant: 73% male adult: 60% female adult: 40-50% Old age 45% Percentage of the water in the body Jj  Functions of Body Water Main Functions: Solvent Transport Other Functions: Give shape and form to the cells Regulate body temperature Joint lubricant Cushion body organs (e.g. CSF for CNS) Functions of Body Water  FLUID COMPARTMENTS EXTRA CELLUAR INTRA CELLULAR FLUID FLUID INTERSTITIAL TRANSCELLULAR PLASMA FLUID FLUID CSF Intra ocular Pleural Peritoneal Synovial Digestive Secretions  Body Water Distribution Intracellular Interstitial Plasma Body Water Distribution TBW = 0.6 x 70 Kg (Body Weight in adult male) = 42 L  Body Water Distribution TBW = 0.6 x Body Weight in adult male (70 Kg) Interstitial fluid: it is the fluid that bathes and surrounds the cell Transcellular fluid : it is portion of fluid contained spaces between 2 epithelial lines eg: cerebrospinal fluid, pleural. fluid  COMPOSITION OF BODY FLUIDS CATIONS (mmol/l) Plasma Interstitial Intracellular Na 142 139 14 K 4.2 4.0 140 Ca 1.3 1.2 1 × 10−4 Mg 0.8 0.7 20 ANIONS (mmol/l) Cl 108 108 4.0 HCO3 24.0 28.3 10 Protein 1.2 0.2 4.0 HPO4 2.0 2.0 11  ECF is mainly high in Na, Cl, and bicarbonate. In addition to Oxygen transported from lungs to blood, carbohydrates, amino acids and fatty acids. ICF is mainly high in K, Mg, and Phosphate. There are special mechanisms are responsible to maintain the ionic difference between ECF and ICF.  COMPOSITION OF BODY FLUIDS There are special mechanisms responsible for the ionic difference between ECF and ICF. This ionic difference plays an extremely important role in neuronal signaling and muscle contraction. ECF contains all the essential nutrients and ions needed by the cells to maintain optimum cell performance. All cells of the body have the same ECF , which represents the internal environment of the body. ECF is in continuous motion throughout body, as transported rapidly in blood vessels and mixed between blood and interstitial (intercellular) fluid by diffusion through the capillary walls. Normal Daily Inputs and Outputs Input mL Output mL Drink 1500 Urine 1500 Food 750 Faeces 100 Metabolic 350 Lungs 400 Skin 600 Total 2600 Total 2600  Water Balance Water balance: Input = output Dehydration is an abnormal reduction of the major fluid volumes Overhydration is an abnormal increase of total body water  Homeostasis Homeostasis is keeping the internal environment relatively constant (dynamic steady Internal Environment state) is the extracellular fluid  Homeostasis Constant (dynamic steady state) Input or gain = output or loss  Why do we need a nearly constant internal environment? For proper function of the living cells Disturbed homeostasis leads to disturbance of the functions of body organs. Factors that are homeostatically regulated Concentration of nutrient substances Concentration of O2 and CO2 Concentration of water and electrolytes Temperature, pH, blood pressure Elimination of waste products Setpoint for each biological variable Body temperature 37 oC Heart rate 70 beat/minute Respiratory rate 16 breath/minute Blood pressure 120/80 mmHg Arterial blood pH7.4 Plasma Na+ 142 (mEq/L) Plasma osmolarity 290mosm/L Components of Reflex Control  Homeostatic control systems are operating by negative feedback The action taken opposes the change in the variable. It leads to maintaining steady state (keeping the variable around the set point) Components of Homeostatic Control Systems Water Balance 24 Positive Feedback is another type of Feedback Control systems The action taken reinforces or amplifies the change in the variable. It does not help homeostasis in most conditions. It produces a vicious cycle could lead to death. Examples: When blood pressure decreases and blood flow to coronary arteries of heart decreases. Positive feddback causes more falling in blood pressure and more dcrease in coronary blood flow and more weakness in heart muscle.  Positive feedback Sometimes, positive feedback plays a role in maintaining homeostasis like labour, nerve signals, and hemostasis (plug formation in cutting blood vessel.  Positive Feedback control Example 1 Uterine contractions during labor Positive Feedback control Example 2: Blood coagulation